Ab0721 Influence of a Proinflammatory Environment on the Expression of Receptors or Transporters of the Metabolites Lactate and Succinate in Pathophysiological Effector Cells in Rheumatoid Arthritis

Background: Synovial lactate and succinate levels as well as the levels of lipopolysaccharide (LPS) and several cytokines are increase in the serum of patients with rheumatoid arthritis (RA) in comparison to healthy controls. While the increased lactate and succinate levels are caused by metabolic changes, intestinal dysbiosis and an increased permeability of the intestinal barrier are discussed as major contributing factors to the increased LPS levels. For various pathophysiologically relevant cells in RA, such as macrophages, effects of lactate and succinate have previously been observed. LPS with its strong proinflammatory effect was able to accelerate and reactivate experimentally induced arthritis in mouse models. In RA patients, an association between disease activity and LPS bioactivity within serum could be shown. Objectives: To analyze whether a proinflammatory environment, being created by molecules such as IL-1β, TNF-α and LPS, affects the expression of transporters and/or receptors of lactate and succinate, and whether the LPS-induced IL-6 secretion of RA synovial fibroblasts (SF) can be reduced by chemical inhibitors of the lactate transporters. Methods: The cell line THP-1 (monocytes), Jurkat (T cells) and Toledo (B cells) as well as primary RASF were stimulated with the cytokines IL-1β and TNF-α or LPS. The expression of the lactate transporters MCT1 and MCT4, the lactate receptors GPR132 and the succinate receptor GPR91 were determined by real-time PCR. LPS-stimulated RASF were additionally treated with chemical inhibitors against MCT1 (AZD3965) and MCT4 (syrosingopine, preferential MCT4 inhibitor). The cellular secretion of IL-6 was quantified by ELISA. Results: While the expression of the lactate transporters MCT1 was unaffected by IL-1β, TNF-α and LPS, the expression of the lactate transporter MCT4 was increased in RASF by LPS to a level 5 times higher than its basal level (n=7). IL-1β reduced the expression of the lactate receptor GPR132 by a factor of 2 in Jurkat and Toledo cells, while GPR132 expression in other cell types did not show any clear changes (n=1 each). The succinate receptor GPR91 of THPS-1 was reduced by TNF-α and LPS in its expression by a factor of 2, while IL-1β increased its expression by a factor of 2 in Jurkat and Toledo cells (n=1 each). As expected, LPS alone caused an increase of IL-6 secretion by RASF. However, the IL-6 secretion of LPS-stimulated RASF was not reduced but instead elevated by the lactate transport inhibitors AZD3965 and syrosingopine (n=4). Conclusion: A proinflammatory environment appears to differentially affect the expression of the transporters or receptors of lactate and succinate depending on the cell type and the proinflammatory factor. The increased MCT4 expression of RASF in comparison to SF of osteoarthritis patients might at least partially be caused by alterations of systemic LPS levels. The application of chemical MCT inhibitors is probably not suited for suppressing the LPS-induced IL-6 secretion of RASF. REFERENCES: NIL. Acknowledgements: NIL. Disclosure of Interests: None declared.